Sensors generate detectable signals upon interaction with a magnitude to be sensed. The signal level is representative of the sensed magnitude, in order to have a good readout. Usually signals are obtained from charges generated in the sensing element as a response to the sensed magnitude. For example, photocharges are generated in radiation sensors (such as infrared, optical, UV sensors . . . ) when radiation impinges on the sensing element or elements in the sensor. These charges need to be measured, for example by converting the charge to a readable signal such as voltage, which is easy to extract and manipulate. Many circuit configurations with different elements exist for performing this conversion. For example, some circuits including amplifiers, such as the capacitor transimpedance amplifier (CTIA), are used in sensing applications for charge-to-voltage conversion.
However, these circuits are typically optimized for obtaining a good signal at either high levels or low levels of the magnitude to be sensed (high levels or low levels of radiation). If a sensor including a circuit for a predetermined range of measurement levels is exposed to different levels outside of this range, the accuracy of the readout drops, so the results will not be exact. For example, a radiation sensor optimized for low levels of radiation will saturate and stop giving meaningful readout of the signal, because the saturated signal level is not representative of the sensed magnitude anymore. On the other hand, a radiation sensor optimized for high levels of radiation will present a readout with a high noise level if the radiation levels are low.
Thus, it would be desirable to obtain a sensing element with good tolerance against saturation, and still presenting good response to low radiation levels.